Method for effecting low-loss torque transmission in planetary gears

ABSTRACT

The invention relates to a method for effecting torque transmission in a single-stage planetary gear comprising 2-6 planet units. The arrangement and the interaction of individual gear elements in conjunction with a method for mounting and adjusting them result in a torque transmission with uniform load distribution to the individual planet units.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to a method for the low-loss and low-noisetransfer of a torque, introduced into a transmission at low rotationalspeed via an input shaft, to an output shaft of comparatively highrotational speed in a single-stage epicyclic transmission having aplurality of planetary units.

Mechanical transmissions serve for transferring a torque introduced viaa drive shaft to an output shaft in as loss-free, operationally reliableand cost-efficient a manner as possible in fulfillment of variousboundary conditions. Predetermined boundary conditions relate to theconstruction dimensions or the available space provision, the magnitudeof the torque to be transferred, the predetermined shaft rotationalspeeds during input and output, but also the degree of lack of noise, ofoperational reliability and of uniform utilization, and the designrequirements for simple assembly and maintenance of the transmission.

Power losses in slow-running transmissions are predominantly frictionallosses caused by axial and/or radial forces between meshing gearwheelsand at shaft bearings.

In line with the importance of this, therefore, a multiplicity ofproposals for minimizing torque losses in transmissions are known, theboundary conditions which were referred to above and have to be takeninto account making it necessary to reach compromises.

Transmission gearwheels are designed with a straight or a helicaltoothing. To compensate axial forces and to minimize power losses inbearings, helical toothings are designed as double or herringbonetoothings, that is to say a gearwheel or a gearwheel unit has twobeveled tooth halves contiguous to one another or two half wheelsforming a unit and beveled correspondingly in the toothed region.

A specific group of transmissions comprises stepped planets. These areunderstood to mean transmissions with one planetary unit or, for thepurpose of torque distribution or load distribution, preferably aplurality of planetary units which rotate about their own planet shaftand which, if appropriate, additionally orbit around the shaft of atransmission component central to the planetary unit with a sun pinion(stationary transmission/planetary transmission). The planetary unitalways co-operates, in the transmission, with a torque-input and atorque-output transmission component, for example with a ringwheel andwith a sun pinion. Two gearwheels or gearwheel units having differentnumbers of teeth are arranged on the shaft of a planetary unit so as tobe spaced apart from one another and fixedly in terms of rotation withrespect to one another. Stepped epicyclic transmissions make it possibleto have a higher ratio in a transmission step than epicyclictransmissions with single planets. They also have fewer parts thangenuine two-stage epicyclic transmissions and are therefore used. For acompact type of construction, the epicyclic transmissions areconventionally designed with a power split.

In the case of stringent requirements regarding the quiet running ofstepped epicyclic transmissions, the teeth of the gearwheels are oftendesigned with a helical toothing. Simple helical toothings lead, duringtorque transfer, to undesirable axial forces between the meshinggearwheels. As a countermeasure, it is known, by the choice of thehelics direction and the size of the helics angle of two planetarygearwheels seated on a planet shaft for load input and load output, tocompensate the axial forces occurring and consequently to keep theresultant axial force of a planetary unit as low as possible. Axialforces and tilting moments not compensated in a planetary unit have tobe absorbed in the shaft bearings of the planetary unit.

During the co-operation of helically toothed planetary units with adrive or output component of the transmission, considerable axial forcesare always transferred to these, particularly also in situations closeto practice where two or more planetary units are used for the powersplit. Furthermore in the mounting of rapidly rotating transmissioncomponents, for example the output component with a sun pinion which,moreover, mostly also is designed to be freely adjustable radially, highaxial forces require a considerable structural outlay in terms ofbearing size and bearing design for absorbing the axial forces. Theresult is undesirable power losses in the bearings.

In the individual planetary units within a stepped planet set, it isnecessary, for uniform load distribution to the individual planetaryunits, with axial forces at the same time being compensated, to have ahighly accurate co-ordination of the angular positions (tooth helics,angular position on planet shaft) of the individual gearwheels. Thisrequires a considerable outlay in terms of manufacture and/or ofassembly. Moreover, for example because of an uneven thermal expansion,changes in axial distance between two gearwheels with a simple helicaltoothing which mesh on different shafts in a transmission have aconsiderable influence on the load distribution to the individualplanetary units arranged around a central unit.

The two gearwheels or double gearwheels of a planetary unit which arespaced apart from one another have hitherto had either a uniformstraight toothing or a uniform helical toothing or double helicaltoothing. Only with regard to these design variants is there sufficientexperience of transmission properties to which a person skilled in theart can refer.

In application of this basic knowledge, familiar to a person skilled inthe art, with regard to the design of an epicyclic transmission and itseffect on axial forces, power losses and load splitting, efforts havebeen concentrated, in the past, either on absorbing the unavoidableforces in as low-loss shaft bearings as possible and/or, for thispurpose, proposing as space-saving designs as possible which arescarcely detrimental to the transmission dimensions or else on takingmeasures to keep axial forces as far away from the shaft bearings aspossible, that is to say to compensate such axial forces, andconsequently to make it unnecessary to have bearings which aretechnically complicated and nevertheless mostly susceptible to repair.

An example of endeavors in the former case is DE 199 17 605 A1. Thisrelates to a transmission capable of being plugged onto a drive shaftand having a multistep planet arrangement. Force input or torque inputtakes place via an internally toothed ringwheel to a first planet stepwith a shaft fixed with respect to the transmission case. On the basisof these technical stipulations, the inventive teaching there relates toa space-saving bearing configuration for the input shaft, including theringwheel attached nonpositively and/or positively on the latter.

Of the multiplicity of known publications with measures for forcecompensation and/or load distribution in epicyclic transmissions, thefollowing are outlined representatively.

To limit the noncompensated axial forces on the drive shaft and outputshaft of a transmission and in order to keep the mounting of theindividual planetary units of a multistep planet as free of axial forcesas possible, the patent specification DE 4017226 A1 proposes the designof a transmission with at least three planetary units distributeduniformally over the circumference, the gearwheels of a planetary unit,which are commonly designed as double split wheels, being connected toone another via an axially elastic clutch. This already technicallycomplicated design additionally requires an axially elastic connectingclutch for the drive shaft and/or output shaft, since the distancebetween the two shafts varies, depending on the unavoidably variableposition of the gearwheels with respect to one another, and, on theother hand, the transmission is not free of axial forces relative to theoutside. The enormous outlay involved in two double helical toothings incombination with the large number of elastic clutches is economicallyjustifiable, at most, in power-split stationary transmissions with outerringwheel and/or at high circumferential speeds.

DE 39 23 430 C2 describes a spur wheel with a double helical toothing,having a herringbone toothing, for an epicyclic transmission with anindividual planetary unit, said spur wheel being designed for simplermanufacture than two individual wheels or half wheels with an opposite,but equal helics angle. The two half wheels are connected to one anotherfixedly in terms of rotation and with profile conformity in one specificoperation. This takes place with the aid of a pressure oil connection atthe connecting press fit of the two half wheels which can thereby beadjusted by being rotated onto a common midplane. The result is asetting of the symmetry of two gearwheel halves with a high structuraloutlay in technical terms. The object of a uniform load distribution tovarious planetary units does not arise because of a lack of a pluralityof planetary units.

DE 199 61 695 A1 relates to an epicyclic transmission, as above withoutload distribution to a plurality of planetary units, with a fixedlymounted fixed wheel which has a double helical toothing and which mesheswith a correspondingly toothed loose wheel, the teeth of each of the twopart regions of the double helical toothing having different helicsangles in such a way that the resultant axial force components built upin a controlled manner during the meshing of these double gearwheelscorresponds to that which acts in the opposite direction and which isintroduced into the transmission via the loose wheel of the outputshaft, for example in the case of an only single helical toothing of thesecond gearwheel rotating together with the loose wheel on the sameshaft. In practice, however, this compensation can only ensure that theloose wheel shaft is free of axial forces relative to the outside andthat the two double helical toothings are centered with respect to oneanother and are subjected to equal stress. The additional difficulty forforce compensation, namely that of a uniform load distribution to aplurality of planetary units, does not arise.

SUMMARY OF THE INVENTION

The object on which the invention is based is, therefore, to propose amethod and a multistep epicyclic transmission suitable for this, whichallows a low-loss and low-noise transfer of a torque introduced at a lowshaft rotational speed to a preferably co-axially oriented output shaftwith high rotational speed, as compared with the input shaft, and whichdoes not have or as far as possible prevents the disadvantages of themethod and transmission designs described above. The object, therefore,is to find an economical method and cost-effective structural devicesfor the as far as possible complete compensation of axial forces in aload-split or power-split transmission with a uniform load distributionto the individual planetary units.

This initially mentioned object is achieved, according to the invention,by means of a method according to the characterizing features of themethod claims. A transmission suitable for this has the features of thedevice claims.

Individual preferred embodiments of the method are described in thesubclaims.

Preferred embodiments of epicyclic transmissions for carrying out themethod are reproduced in FIGS. 1 a and 1 b.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 a illustrates a part region of the transmission according to theinvention as a section through the shaft center point of the co-axialdrive shaft and output shaft. In this version, the gearwheels of aplanetary unit are arranged between the two shaft bearings in the planetcarrier.

FIG. 1 b shows a transmission according to the invention in anillustration identical to that of FIG. 1 a, but with one of the twogearwheels or double gearwheels being arranged outside the two shaftbearings, that is to say with an overhung arrangement of the doublegearwheel with respect to the local position of the bearings on theplanet shaft.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 a shows an epicyclic transmission constructed axiallysymmetrically about the axis (L) and having a co-axial input shaft (8)and output shaft (9) in a sectional plane such that one of a pluralityof planetary units (1) arranged around the sun pinion (4) of the outputshaft (9) is illustrated. The planetary unit (1) is mounted in a planetcarrier (7) fixedly in the radial direction and movably in the axialdirection by means of two bearings (6) and possesses a double gearwheel(5) constructed from two half wheels (5 a) (5 b) and a straight-toothedgearwheel (3). The opposite helical toothing in the half wheels (5 a)and (5 b) is indicated. The half wheels are designed to be spaced apartfrom one another. It was decided to dispense completely with showing oneof the many devices which are familiar to a person skilled in the artand by means of which, in each planetary unit, the second half wheel canbe adjusted and subsequently locked with respect to the first half wheelin the axial direction and/or by rotation relative to one another aboutthe axis. Individual design variants for devices of this type aredescribed further below. The sun pinion (4) with helical toothingcorresponding to the double gearwheel (5) is designed, on the outputshaft (9), as a positively connected and/or materially integralgearwheel unit.

The ringwheel (2) is designed as a positively connected and/ormaterially integral unit with the drive shaft (8).

In FIG. 1 b, as the only difference from FIG. 1 a, the planet shaft of aplanetary unit is mounted in the planet carrier (7) with an overhungarrangement of the double gearwheel (5), specifically with free axialmovability between the planet shaft and bearing (6).

For a person skilled in the art, it has hitherto been the unquestionedmeans of choice in epicyclic transmissions in which the torqueintroduction into a planetary unit takes place via a ringwheel, todesign the meshing gearwheels with helical toothings for reasons ofnoise reduction and vibration reduction.

Surprisingly, according to the invention, these planetary gearwheelsmeshing with the ringwheel can be designed with straight toothingwithout disadvantages for the properties of noise and of vibration. Oneexplanation of this would seem to be the combination of both a lowrotational speed of the input shaft and a high degree of profile overlapin the tooth engagement of a ringwheel with the planetary gearwheels ofall the planetary units according to the invention. It is conducive oreven indispensable for these favorable noise properties to havesimultaneously the design, essential to the invention, of a doublehelical toothing and, further, the adjustability according to theinvention of the half wheels of the double gearwheel of all theplanetary units which mesh with the sun pinion. The advantage whicharises is especially appreciable, because, in the case of the sunpinion, there is a state in which there is a low degree of profileoverlap and which is unfavorable for noise generation.

In the design of the sun pinion, it is absolutely essential for it to beconfigured with a helical or double helical toothing. On the one hand,in the case of the sun pinion, the tooth circumferential speed ismarkedly higher, as compared with that during the tooth engagement ofthe ringwheel with the planetary gearwheel, specifically by the amountof the ratio of the rolling circles of the two identically rotatinggearwheels of a planetary unit, and, on the other hand, the profileoverlap is low here, as compared with the situation during the toothengagement between the ringwheel and multistep planet, since, in thecase of the sun pinion, there is an external gearwheel with a regularlylarge difference in number of teeth in relation to the meshing gearwheelof the planetary unit. Purely with regard to noise generation, thedouble helical toothing is equivalent to the single helical toothing ofcomparable construction width.

The axial positioning of the planetary units (1) and sun pinion (4) inrelation to one another is determined either by a fixed mounting of thesun pinion (4) or else by the fixed mounting of only one of a pluralityof planetary units (1), this being in conjunction with the adjustment ofthe half wheels of the remaining planetary units.

The orientation or adjustment of the two half wheels (5 a, 5 b) of thedouble gearwheel takes place in the form of a relative rotation and/orby means of an axial displacement of the half wheels with respect to oneanother.

According to a preferred embodiment of the invention, the two halfwheels are screwed together frictionally. The screw shanks have play inthe passenger bores. The tooth pitch position of the two half wheels isadjusted as a result of the relative rotation of the latter within theplay of the screw shanks in the passenger bores.

Any change in axial distance between the half wheels means at the sametime a relative rotation of the tooth positions with respect to oneanother. According to a further preferred embodiment of the invention,adjustment by means of an axial displacement of the half wheels (5 a, 5b) with respect to one another takes place by the insertion of adjustingplates 10 between the half wheels on the planet shaft in order toachieve a uniform bearing contact of the tooth flanks of the two halfwheels.

The possibility of adjustment by means of corresponding elements anddevices performs a further advantage. It allows a less exact andtherefore more cost-effective manufacture of the individual transmissiongearwheels and components. This all the more so when the two adjustingmethods described above are combined.

The adjustment of the two half wheels (5 a, 5 b) of the double gearwheelof a planetary unit with respect to one another must lie within therange of the pitch accuracy of the gearwheels themselves, in order, inthe case of a plurality of planetary units (1), to achieve a uniformload distribution to the individual units. Adjustment takes place duringassembly, specifically, depending on the prevailing conditions, on thealready installed planetary unit or outside the transmission on anadjusting device provided for this purpose and simulating the planetcarrier. The latter alternative, however, entails the checking ofuniform tooth carrying in the transmission. The change, regularlyaccompanying the adjustment, in the axial position of a planetary unit(1) with respect to the ringwheel (2), in the case of the axiallyretained sun pinion (4), does not cause any disturbance, however, sincethe straight toothing of the planetary gearwheel (3) which is inengagement with the ringwheel (2) does not give rise, during an axial orlongitudinal displacement of these two gearwheel units on a shaft inrelation to one another, to any change in angle of rotation with respectto one another, in contrast to the situation where the helical toothingis used. Once the tooth engagement positions of the individual planetaryunits have been adjusted in terms of optimum force distribution, achange in length of the shaft between the gearwheels of an individualplanetary unit, but also between those of different planetary units,does not lead to any change in the load distribution to the individualtooth contacts. Also, in the design of the features of the invention,the position of the tooth pitch of the first half wheel (5 a) of thedouble gearwheel (5) has to be assigned to that of the gearwheel (3)with a straight toothing only to an extent such that there is no axialrun-on of gearwheels during operation and that all the gearwheels carryover their entire width. In order to ensure this, according to knowntransmission configurations, one of the gearwheels meshing in each caseis designed to be wider than the other, and the half wheels of thedouble gearwheel are not laid directly against one another, but possessan axial gap between one another.

In the overhung arrangement of the double helical toothing according toFIG. 1 b, a mounting, including adjustment, of the double helicaltoothing is still possible in a comparatively simple way. An arrangementwith the mounting of a planet shaft on both sides outside thegearwheels, according to FIG. 1 a, may, inter alia in the case of asmall diameter of the double gearwheel, make it markedly more difficultto carry out mounting and subsequent adjustment in the transmission.Consequently, according to a further preferred version, the transmissionaccording to the invention may possess a divided planet carrier (7) suchthat the planetary units already preadjusted outside the transmissioncan be introduced into the bearings (6) in the planet carrier (7) ineach case radially with respect to the planet shaft, for a trialmounting and checking of the tooth position in relation to the alreadyinstalled and adjusted planetary units and for further removal andreadjustment.

In a preferred embodiment for carrying out the method according to theinvention, the planet shaft is configured in its profile according tothe straight-toothed planetary gearwheel. This profile form is continuedover the width of tooth engagement with the ringwheel and, there, whenshortened tooth tips, and the half wheels of the double gearwheel areplugged with a geometrically corresponding inner profile onto the planetshaft thus toothed and are adjusted and locked. The adjustment of thehalf wheels in this case takes place solely by the variation andco-ordination of the axial distance between the two half wheels of thedouble gearwheel.

The method according to the invention can be used, in particular, inepicyclic transmissions for wind power plants, but is not restricted tothis application.

In a way which can easily be understood by a person skilled in the art,identical actions and advantages can be achieved when the drive shaftand output shaft are interchanged in their function, that is to say whena torque is introduced with a high shaft rotational speed into theoutput shaft now serving as a drive shaft and is taken off with a lowshaft rotational speed via the previous drive shaft, now the outputshaft. The latter form of torque transfer is a likewise preferredembodiment of the present invention.

1. A method of mounting gears for transfer of an introduction torqueintroduced into a transmission at a comparatively low shaft rotationalspeed to an output shaft of comparatively high rotational speed in asingle-step epicyclic transmission with a plurality of planetary units,the method which comprises: transferring the introduction torque via aninternally straight-toothed ringwheel to a plurality of two to sixplanetary units fixedly mounted radially with respect to one another ina planet carrier and to an oppositely helix-toothed sun pinion of theoutput shaft; rigidly connecting a straight-toothed planetary gearwheelmeshing with the ringwheel and one of two oppositely helix-toothed halfwheels of a double gearwheel, meshing with the sun pinion, of eachplanetary unit to one another on a planet shaft; and assemblingindividual planetary units into bearings of the planet carrier, andthereby placing a respective second half wheel relative to the firsthalf wheel, by way of devices for axial and/or rotational displacement,into a position of predetermined tooth carrying and load distributionbetween the individual planetary units and locking the second half wheelin the position.
 2. The method for torque transfer according to claim 1,which comprises effecting the axial and/or rotational displacement ofthe second half wheel successively on each of the individual planetaryunits.
 3. The method for torque transfer according to claim 1, whichcomprises assigning the position of the first half wheel of the doublegearwheel to the second half wheel of the double gearwheel by rotatingthe first and second half wheels relative to one another.
 4. The methodfor torque transfer according to claim 1, which comprises assigning theposition of the first half wheel of the double gearwheel to the secondhalf wheel of the double gearwheel by axially displacing the first andsecond half wheels relative to one another.
 5. The method for torquetransfer according to claim 1, which comprises, following a positionassignment, connecting the second half wheel to the planet shaft and/orto the first half wheel and locking the second half wheel in thatposition.
 6. The method for torque transfer according to claim 5, whichcomprises using a force-locking connection for connecting the secondhalf wheel to the planet shaft and/or to the first half wheel.
 7. Themethod for torque transfer according to claim 5, which comprises using aform-locking connection for connecting the second half wheel to theplanet shaft and/or to the first half wheel.
 8. The method for torquetransfer according to claim 1, which comprises locking the second halfwheel axially resiliently with respect to the first half wheel.
 9. Themethod for torque transfer according to claim 1, which comprises using atoothing profile of the straight-toothed planetary gearwheel, with a tipthereof shortened, as a shaft profile for the axial guidance of one orof both half wheels by way of a corresponding inner profile on theshaft.
 10. The method for torque transfer according to claims 1, whichcomprises adjusting the second half wheel in axial direction withrespect to the first half wheel by inserting adjusting plates betweenthe first and second half wheels.
 11. The method for torque transferaccording to claims 1, which comprises introducing the planetary unitsinto bearing points in a divided planet carrier radially with respect toan axial direction of the planet shaft.
 12. A single-step epicyclictransmission for transferring a torque introduced at a comparatively lowrotational speed onto an input shaft to a sun pinion of an output shaftwith a comparatively high rotational speed, comprising: a planetcarrier; a plurality of planetary units mounted radially fixed withrespect to one another on said planet carrier; an oppositelyhelix-toothed double gearwheel formed with two half wheels; eachplanetary unit having a planet shaft and a straight-toothed planetarygearwheel fixedly connected to said two half wheels, saidstraight-toothed planetary gearwheel meshing with a ringwheel connectedfixedly to the input shaft and having an internal straight toothing;each planetary unit including devices configured, during mounting ofindividual said planetary units in said planet carrier, to orient saidsecond half wheel, for uniform load distribution to all said planetaryunits, with respect to said first half wheel in an axial directionand/or by rotation about the planet shaft and to lock said second halfwheel.
 13. The transmission according to claim 12, wherein saidplurality of planetary units include two to six planetary units.